I also have both.
The mpx is so fun to shoot, but cleaning is more important and about 3 times more work. I don't think at my level it makes any difference to scores (A class) as long as gun runs reliably.
I have had issues with reliability with JP when using Goliath mag extensions, polymer bullets, and short stroking. I think I got resolved by cleaning up mag body transition and follower.
Mpx had reliability issues until I upgraded extractor.
At this point both guns run.

I have 4 sets of pro ears for self, wife, son. Every year or so a band breaks and they send me a replacement no questions asked for free. I bought a pair of msa sordins recently and I can't believe what I was missing. Much better audio quality and increased comfort from sordins but at much more money.

This is data over 2 months.
Started with SWMP, loaded a bunch until I was out of powder. Then I bought 115's and couldn't test SWMP with 115s.
Next, I tried HS6 with both 124's and 115's and I liked the 115's, so I bought a case of those.
Now I am trying my new AA7 115 loads vs the SMWP 124 loads I loaded up originally.
I had fewer shots when I captured SD/ES for SWMP so I didn't consider the numbers valid. This is not as scientific as it could be, but it is what I have.
Josh

Walther sent me a replacement captured guide rod with lower power spring when I called saying I was having issues with low power factor rounds. The only mod the trigger needs is in the trigger safety spring if you have a very high grip.

I called Walther and they sent me red spring vs the unpainted spring that was in the gun at no cost (would have been $32 if they had charged me). The gun feels normal to rack now, vs. before when it felt unusually difficult to rack compared to my other pistols. I haven't yet shot it to see if it clears up my stove pipes I was having with my 130 PF ammo. I am happy with my Walther customer support so far, although I wish I could just buy an uncaptured guide rod so I could use a spring of my choice.

How would the new trigger affect production? If I buy the SF then put in this trigger it will only be production legal after the new gun with this trigger has sold enough to be production eligible? Will it have a separate model number preventing that?

ATF said in 2017 that it isn't illegal to shoulder lacking other intent e.g. permanent attachment, removing strap, etc. Of course they can reverse this whenever they want as they are doing with bumpstocks.
“With respect to stabilizing braces, ATF has concluded that attaching the brace to a handgun as a forearm brace does not ‘make’ a short-barreled firearm because … it is not intended to be and cannot comfortably be fired from the shoulder.” The letter continues: “Therefore, an NFA firearm has not necessarily been made when the device is not re-configured for use as a shoulder stock — even if the attached firearm happens to be fired from the shoulder.”
I agree that uspsa should make it legal to use a brace, it simplifies carrying across state lines. It doesn't give the competitor any advantage vs. a stock.
I have an MPX SBR I used in competition, but bought a JP with pinned and welded comp to avoid having to file paperwork when I leave my state.

My Red Hill holster shipped today, order placed 1/20.
The more interesting thing is I ordered the holster after I told my dealer to place an order for the gun. I will have my holster Wednesday but no idea when I will get the gun. My dealer claimed it is unobtainium.